Door-to-door work teaches you that a closed door is just a door. There’s another one next to it.

Repeated refusal teaches something that cannot be reasoned into you: that a no is an event, not a statement about your worth, and that it is immediately followed by another opportunity. The first few land personally. After enough of them the whole category shrinks to the size it deserves.

Put yourself somewhere that involves being turned down regularly, even for a short stretch. Keep going to the next one without pausing to analyse the last. The lesson is in the volume rather than in any single attempt.